In the medical field, where beneficial agents are collected, processed and stored in containers, transported and ultimately delivered through tubes by infusion to patients, there has been a recent trend toward developing materials useful for fabricating such containers and tubing without the disadvantages of currently used materials such as polyvinyl chloride (PVC). These new medical tubing materials must have a unique combination of properties, so that the tubing can be used in fluid administration sets and with medical infusion pumps. These materials must have good bonding properties, sufficient yield strength and flexibility, be environmentally friendly and compatible with medical solutions, and exhibit little post-autoclave coil set. In addition, to be commercially viable, the tubing must be extrudable at high speeds, greater than 50 ft/min.
It is a requirement that the tubing be environmentally compatible as a great deal of medical tubing is disposed of in landfills and through incineration. For tubing disposed of in landfills, it is desirable to use as little material as possible to fabricate the tubing. To this end, it is desirable to use a material which is thermoplastically recyclable so that scrap generated during manufacturing may be refabricated into other useful articles.
For tubing that is disposed of by incineration, it is necessary to use a material that does not generate or minimizes the formation of by-products such as inorganic acids which may be environmentally harmful, irritating, and corrosive. For example, polyvinyl chloride may generate objectionable amounts of hydrogen chloride (or hydrochloric acid when contacted with water) upon incineration, causing corrosion of the incinerator and possibly presenting other environmental concerns.
To be compatible with medical solutions, it is desirable that the tubing material be free from or have a minimal content of low molecular weight additives such as plasticizers, stabilizers, and the like. These components could be extracted by the therapeutic solutions that come into contact with the material. The additives may react with the therapeutic agents or otherwise render the solution ineffective. This is especially troublesome in bio-tech drug formulations where the concentration of the drug is measured in parts per million (ppm), rather than in weight or volume percentages. Even minuscule losses of the bio-tech drug can render the formulation unusable. Because bio-tech formulations can cost several thousands of dollars per dose, it is imperative that the dosage not be changed.
Bonding properties are important because medical tubings are often connected to a port of an I.V. container or a continuous ambulatory peritoneal dialysis (CAPD) container or other junction components within a fluid administration set. Therefore, it is necessary that the tubing be capable of attaching to polymers such as polyesters, polycarbonates, and polyolefins which are commonly used to fabricate such junctions.
Autoclavable medical tubing must be flexible. The majority of autoclavable medical tubings are produced from polyvinyl chloride. Because polyvinyl chloride by itself is a rigid polymer, low molecular weight components known as plasticizers must be added to render polyvinyl chloride flexible. However, these plasticizers may be extracted out of the tubing by the fluid. For this reason, and because of the difficulties encountered in incinerating polyvinyl chloride, there is a need to replace polyvinyl chloride medical tubing.
The tubing must also exhibit very little coil set and a small spring constant after autoclave. Coil set is a phenomenon where the tubing retains a helical shape after it has been unwound from a spindle or the like. Coil set is a problem because it causes the tubing to be physically shortened. In addition, a tubing exhibiting coil set possesses a degree of potential energy when it is straightened for use. When the tubing is used to connect an I.V. or a CAPD container to a patient, the potential energy creates an undesirable pulling force on the exit site of the patient. The pulling force can cause pain and discomfort to the patient, and eventually, infection may occur.
Non-polyvinyl chloride tubings are available; however, these tubings are not suitable for applications where flexibility and sealing rely on the elastic properties of the tubings. For instance, oil-modified styrene-ethylene-butene-styrene (SEBS), such as Kraton G2705 manufactured by Shell Chemical Company, has the necessary flexibility, but tubings produced from Kraton G2705 cannot be manufactured at a high rate due to extremely poor melt strength caused by phase separation at the extrusion temperature. This phase separation causes the Kraton G2705 tubings to melt fracture. Thus, as the tubing produced from Kraton G2705 is extruded at commercial speeds, it breaks into pieces.
U.S. Pat. No. 4,041,103 (Davison et al.) and U.S. Pat. No. 4,429,076 (Saito et al.) disclose non-polyvinyl chloride polymeric blends of a polyamide and SEBS. However, the polymeric materials of these patents generally fail to provide the physical properties required for medical tubings. For example, Davison et al. discloses illustrative blends of various combinations of block copolymers, with nylons, and in some cases other components such as polypropylene and ethylene vinyl acetate copolymers. The majority of the blends of Davison et al. specify using nylon 6. The polymeric materials of Davison et al. are more suited to end uses which are subjected to high temperature oxidation environments such as automotive under-the-hood applications or electrical power cable applications. (Col. 6, line 67 to col. 7, line 3).
Saito et al. discloses a polymeric material having 1% to 99% SEBS and the balance being a polyamide. The polymeric compositions of Saito et al. are typically injection or blow molded into automobile parts, electrical parts, mechanical parts, medical equipment, packaging materials, and building materials. (Column 16, lines 46-50).
Others have used SEBS in tubing and films as a component in a blend. U.S. Pat. No. 4,803,102 (Raniere et al.) and U.S. Pat. No. 5,356,709 (Woo et al.) disclose multilayered structures where SEBS blends are used as a layer within the multilayered structures.
For instance, Raniere et al. discloses a multi-layer packaging film. The outer or heat sealing layer being produced from a mixture of not less than 10% by weight polypropylene and up to 90% by weight SEBS. Similarly, Woo et al. discloses a multi-layered tubing. The outer layer of the tubing is produced from a blend of 40 to 99% by weight polypropylene and 1 to 60% by weight SEBS.
Neither Raniere et al. nor Woo et al. disclose using a polypropylene and SEBS blend as a monolayer tubing. Further, neither Raniere et al. nor Woo et al. disclose using a high melt strength polypropylene in its polypropylene and SEBS layer.
The present invention is provided to solve these and other problems.